抄録
In order to investigate the reasons for the variation in the properties or the polymorphic transition behavior of semisynthetic fatty suppository bases, fatty acid composition, melting point, IR value and the transition rate were measured for many kinds of commercial brands and batches. Then, the mutual relations of the above characteristics were examined. It was found that IRmax, the IR value of the most stable crystal form, was correlated with both the melting point and the content of higher fatty acids such as stearic acid and/or palmitic acid. However, the transition rate did not show any special relation with IRmax, but was well correlated with the contents of lower fatty acids, such as caprylic acid and/or capric acid. These tendencies were also confirmed by the results of a fractionation experiment on Witepsol H-15, performed to investigate the above phenomena in more detail. In this experiment, it was observed that the X-ray diffraction pattern and IR value of the physical mixture prepared from the fractionated samples coincided with those of the intact Witepsol H-15 in the cases of both stable and unstable crystal forms. These results suggest that the vehicle is constituted of many kinds of unit crystal cells differing in fatty acid composition, crystalline mode and physical properties. Thus, it was considered that the observed change of X-ray diffraction accompanying the A-to-B transition was mainly due to the higher melting point unit cells and that the transition acceleration was due to the lower melting ones.
